1. Field of the Invention
The present invention relates to a dispersant compound and a method for preparing the same. More specifically, the present invention relates to a novel oligomeric compound with improved dispersion performance, which comprises a tail structure consisting of hydrophilic and hydrophobic blocks and an amine or imidazole head structure, and a method for preparing the oligomeric compound.
2. Description of the Related Art
Dye-sensitized solar cells are photoelectrochemical solar cells that are essentially composed of photosensitive dye molecules capable of absorbing visible light rays to form electron-hole pairs and a transition metal oxide for transferring the generated electrons.
Such dye-sensitized solar cells comprise a semiconductor electrode, an electrolyte, and a counter-electrode wherein the semiconductor electrode consists of a transparent conductive substrate, and a light-absorbing layer including a metal oxide and a dye.
Generally, the semiconductor electrode is produced by forming a metal oxide film on a substrate, and adsorbing a dye on the surface of the metal oxide film. Specifically, the semiconductor electrode is produced by the following procedure. First, a paste composition comprising particles of a metal oxide is applied to a transparent substrate. The paste composition is formed into a metal oxide film by high-temperature annealing at 400-550° C. The metal oxide film is treated with a solution containing a dye for a specified time to adsorb the dye on the available surface of the metal oxide film, thus completing production of the final semiconductor electrode.
According to the general method for producing the semiconductor electrode, since the dye is adsorbed after the metal oxide film is formed on the substrate, the overall surface area of the metal oxide particles is not sufficiently utilized. That is, the area occupied by the dye adsorbed on the metal oxide particles is very small when compared to the optical cross-section of light such that low power conversion efficiency of the solar cells is caused.
When nanoparticles are used to form the metal oxide film, they tend to aggregate within the paste composition. The aggregation of the nanoparticles can lead to a deterioration in uniformity and a low density for the metal oxide film, which in turn can cause low power conversion efficiency in the solar cells.
To address this, many attempts have been made to solve the problems of conventional dye-sensitized solar cells. For example, Korean Patent Laid-open No. 2005-82624 discloses a dye-sensitized solar cell with improved power conversion efficiency, which comprises a semiconductor electrode produced by forming a porous metal oxide film by an electrochemical process using a surfactant, and with a dye adsorbed on the metal oxide film. Further, Japanese Unexamined Patent Publication No. 2002-50413 discloses a dye-sensitized solar cell which comprises an optical semiconductor layer containing porous optical semiconductor particles, wherein the porous optical semiconductor particles are prepared by firing an optical semiconductor powder together with a surfactant or a hydrophilic polymeric compound and dispersion medium at 400° C. or higher, followed by crushing this admixture to form the porous optical semiconductor particles.
According to the conventional dye-sensitized solar cells, however, a surfactant or a dispersant is simply added to a metal oxide powder or optical semiconductor particles and the mixture is formed into a metal oxide film. The introduction of the surfactant advantageously increases the porosity of the metal oxide or the optical semiconductor particles, which in turn allows for the amount of dye that can be adsorbed to be increased and thereby improves the uniformity of the metal oxide film to some extent. However, problems still remain in that since the dye is adsorbed after the metal oxide film or semiconductor layer is formed, the overall surface area of the metal oxide particles is not fully or sufficiently utilized, and as a result, the amount of the dye adsorbed does not substantially or satisfactorily increase and the power conversion efficiency of the solar cells does not therefore improve any further.
There is thus a need to develop a new dispersant that can overcome the above-mentioned problems.